Sprayers, such as backpack sprayers are used across an array of applications, including farms, golf courses and residential properties, to apply water or other liquids, such as fertilizers or pesticides including herbicides, insecticides and the like. As the name implies, backpack sprayers are designed to be worn by the user, such as through securing a tank of the sprayer against the user's back via one or more shoulder straps. A handheld spray wand is fluidly coupled to the tank and is manually actuated, such as through a trigger, to dispense fluid from the tank through the spray wand. To pressurize the fluid for delivery to the wand, backpack sprayers include a pump and may be configured as battery powered pump sprayers or manually actuated pump sprayers.
Typically, manually actuated pump sprayers include pump units suspended beneath the spray tank. A support stand may be included with the backpack to prevent resting of the pump unit on the ground when the sprayer is not being worn. Nevertheless, because the pump unit is located externally of the spray tank, the various moving components of the pump unit are susceptible to impact damage and contamination due to dust and dirt. While backpack sprayers have been engineered to incorporate the pump unit with the body of the tank housing, such sprayers require complex plumbing, are susceptible to seal failures and are difficult to clean and maintain.
A further drawback of manually actuated internal pump sprayers is inefficiency of the pumping mechanism. That is, internal pump sprayers use a single action piston pump to pressurize fluid from the spray tank into the pump's pressure vessel. As a result, actuation of the pump handle pressurizes fluid only on either the up-stroke or down-stroke of the piston. A further consequence is the need for a relatively large-sized piston and cylinder to move a useful amount of liquid per stroke cycle. However, handle force to actuate the pump increases as a result of cylinder diameter. Thus, a large piston and cylinder requires a higher pumping force applied to the handle. The need to provide such a pumping force may lead to user fatigue. Also, the maximum pressure a fluid within the pressure vessel can reach is limited by the amount of handle force required. As a result, large piston and cylinder pumps have decreased operating fluid pressures.
Thus, there remains a need for a backpack sprayer with in an internal pump that is more easily plumbed, operated and cleaned, as well as being more efficient while requiring less handle force. The present invention satisfies this as well as other needs.